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Microbes are responsible for cycling carbon (C) through soils, and predicted changes in soil C stocks under climate change are highly sensitive to shifts in the mechanisms assumed to control the microbial physiological response to warming. Two mechanisms have been suggested to explain the long-­ term warming impact on microbial physiology: microbial thermal acclimation and changes in the quantity and quality of substrates available for microbial metabolism. Yet studies disentangling these two mechanisms are lacking. To resolve the drivers of changes in microbial physiology in response to long-­ term warming, we sampled soils from 13-­ and 28-­ year-­ old soil warming experiments in different seasons. We performed short-­ term laboratory incubations across a range of temperatures to measure the relationships between temperature sensitivity of physiology (growth, respiration, carbon use efficiency, and extracellular enzyme activity) and the chemical composition of soil organic matter. We observed apparent thermal acclimation of microbial respiration, but only in summer, when warming had exacerbated the seasonally-­ induced, already small dissolved organic matter pools. Irrespective of warming, greater quantity and quality of soil carbon increased the extracellular enzymatic pool and its temperature sensitivity. We propose that fresh litter input into the system seasonally cancels apparent thermal acclimation of C-­ cycling processes to decadal warming. Our findings reveal that long-term warming has indirectly affected microbial physiology via reduced C availability in this system, implying that earth system models including these negative feedbacks may be best suited to describe long-­ term warming effects on these soils. 

{"Abstract":["This project is integrating scientific research in the Arctic with education and outreach, with a strong central focus on engaging undergraduate students and visiting faculty from groups that have had little involvement in Arctic science to date. The central element of the project is a month-long research expedition to the Yukon River Delta in Alaska. The expedition provides a deep intellectual and cultural immersion in the context of an authentic research experience that is paramount for "hooking" students and keeping them moving along the pipeline to careers as Arctic scientists. The overarching scientific issue that drives the research is the vulnerability and fate of ancient carbon stored in Arctic permafrost (permanently frozen ground). Widespread permafrost thaw is expected to occur this century, but large uncertainties remain in estimating the timing, magnitude, and form of carbon that will be released when thawed. Project participants are working in collaborative research groups to make fundamental scientific discoveries related to the vulnerability of permafrost carbon in the Yukon River Delta and the potential implications of permafrost thaw in this region for the global climate system.\n This data set includes vegetation biomass and elemental analysis, thaw depth, and point intercept results from the 2019 expedition."]} 

{"Abstract":["This project is integrating scientific research in the Arctic with education and outreach, with a strong central focus on engaging undergraduate students and visiting faculty from groups that have had little involvement in Arctic science to date. The central element of the project is a month-long research expedition to the Yukon River Delta in Alaska. The expedition provides a deep intellectual and cultural immersion in the context of an authentic research experience that is paramount for "hooking" students and keeping them moving along the pipeline to careers as Arctic scientists. The overarching scientific issue that drives the research is the vulnerability and fate of ancient carbon stored in Arctic permafrost (permanently frozen ground). Widespread permafrost thaw is expected to occur this century, but large uncertainties remain in estimating the timing, magnitude, and form of carbon that will be released when thawed. Project participants are working in collaborative research groups to make fundamental scientific discoveries related to the vulnerability of permafrost carbon in the Yukon River Delta and the potential implications of permafrost thaw in this region for the global climate system.\n This data set includes vegetation biomass and elemental analysis, thaw depth, and point intercept results from the 2018 expedition."]} 

High latitude ecosystems are characterized by cold soils and long winters, with much of their biogeochemistry directly or indirectly controlled by temperature. Climate warming has led to an expansion of shrubby plant communities across tussock tundra, but whether these clear aboveground shifts correspond to changes in the microbial community belowground remains less certain. Using bromodeoxyuridine to label growing cells, we evaluated how total and actively growing bacterial communities varied throughout a year and following 22 years of passive summer warming. We found that changes in total and actively growing bacterial community structures were correlated with edaphic factors and time point sampled, but were unaffected by warming. The aboveground plant community had become more shrub-dominated with warming at this site, and so our results indicate that belowground bacterial communities did not track changes in the aboveground plant community. As such, studies that have used space-for-time methods to predict how increased shrub cover has altered bacterial communities may not be representative of how the microbial community will be affected by in situ changes in the plant community as the Arctic continues to warm. 

ABSTRACT Frankiaceae are bacterial endosymbionts that are also found free-living in soil. Here, we present the genome sequences of two novel bacterial members of the order Frankiales , class Actinobacteria , isolated from temperate terrestrial forest soils. The genomes for MT45 and GAS493 indicate a genetic capacity for carbohydrate degradation but not nitrogen fixation. 

ABSTRACT Here, we present the draft genome sequence of a novel species of the genus Singulisphaera (phylum Planctomycetes , family Isosphaeraceae ) isolated from soil. Singulisphaera sp. strain GP187 has a relatively large mobilome and numerous novel genes that may contribute to the production of bioactive molecules. 

Soils store more carbon than the biosphere and atmosphere combined, and the efficiency to which soil microorganisms allocate carbon to growth rather than respiration is increasingly considered a proxy for the soil capacity to store carbon. This carbon use efficiency (CUE) is measured via different methods, and more recently, the 18O-H2O method has been embraced as a significant improvement for measuring CUE of soil microbial communities. Based on extrapolating 18O incorporation into DNA to new biomass, this measurement makes various implicit assumptions about the microbial community at hand. Here we conducted a literature review to evaluate how viable these assumptions are and then developed a mathematical model to test how violating them affects estimates of the growth component of CUE in soil. We applied this model to previously collected data from two kinds of soil microbial communities. By changing one parameter at a time, we confirmed our previous observation that CUE was reduced by fungal removal. Our results also show that depending on the microbial community composition, there can be substantial discrepancies between estimated and true microbial growth. Of the numerous implicit assumptions that might be violated, not accounting for the contribution of sources of oxygen other than extracellular water to DNA leads to a consistent underestimation of CUE. We present a framework that allows researchers to evaluate how their experimental conditions may influence their 18O-H2O-based CUE measurements and suggest the parameters that need further constraining to more accurately quantify growth and CUE.